The know of a company that just completed a contract in which the existing
USAF fleet of C-5 aircraft had their MADARS system (Malfunction Detection
Analysis and Recording System) upgraded with a PC104-based system running
VxWorks as the RTOS and software applications designed in-house. I think
around 90 aircraft were updated (out of a fleet of around 130 aircraft).

Very few, if any Commercial Off The Shelf (COTS) equipment will meet
MIL-spec for such things as temperature range, vibration, and shock. Few
exceptions exist for equipment used within the confines of manned spaces
such as exist on AWACS and some large, special purpose converted transport
planes. Consider that in an compartment of a jet fighter at 40-80,000'
altitude that isn't climate controlled the temperature can drop
below -40degC/F and continuous vibrations of several g's can exist for
sustained periods of time. I have worked with several modern radar systems
and can assure you that whatever components are used, the interconnects are
most definitely not PC104. They are typically very dense, very tight
fitting connectors with mechanical components added to prevent separation of
boards and backplanes.

Many older systems use proprietary software. Some modern stuff uses things
like VxWorks and RealTime-Linux, though special purpose systems still
abound. Just about every "black box" [most are typically grey not black]
has several "computers" each with a single purpose. More hardware is still
cheaper to debug than multi-tasking software.

At those altitudes the air density is quite low, so I would be more
concerned about the generated heat, since the convection or even
forced air cooling is not going to remove the heat from the components
very effectively.

Even nominally benign environments aren't that benign if it's
a mobile (land, air, sea) application. Low intensity vibrations
can lead to eventual failures.

Like embedded applications elsewhere, military embedded apps
cover a broad range of complexity. Many are little more than
elimination of electromechanical devices that could perform
the same function. Some are excedingly complex such as the
processing done in radars. All tend to be very special-
purpose and there's little in the way of COTS program products
that are applicable.

Another problem with COTS, usually overlooked by government program
managers, is the problem of obscelescence that arises with COTS. When a
custom system is designed for the military (not using COTS), the government
usually retains all of the design information including engineering drawings
and source code. In a pinch (or the next World War) the government could
build copies of the system.

With COTS-based design, the government usually doesn't retain any design
information, therefore when the time comes to reproduce the system (usually
years later), the company that produced the original COTS has gone out of
business or the hardware/software has been discontinued. The result is that
an entirely new design must be generated, along with all of the development
and testing.

Not very realistic to assume that this would work these days, since it
would require recreating the whole infrastructure that was once used
to create the original product.

Assuming some old product used custom made RTL, DTL or TTL chips and
the masks for 2" wafers are stored in a safe place. To start producing
these chips again, you first should build the infrastructure to make
blank 2" wafers and then the facilities to apply the masks to it in
some ancient manner. You would also have to train people to bond the
chips in the original approved method to maintain the reliability etc.

In industrial systems, it is common that the customer requires at
least 10 years of support for the system. In some situations, it may
be feasible to store some critical components for a decade or two, but
of course the capital costs are quite high. As long as the interfaces
are compatible, it makes sense to make new subsystems after a few
years with current technology and swap an old malfunctioning unit with
the current version. This way you will not end up with a stock of
completely outdated systems or components when the contract period
ends.

The important thing is to maintain the interfaces (instruction sets,
protocol frame structures, signal levels, connectors, fixing holes
etc.) for a very long time, not to recreate some historical relics
from the beginning.

What is inside the black block is not important, it could be
implemented using COTS technology, even if the original system used
some custom made subsystems, in order to achieve the required
performance in the old days. When implementing the same subsystem
later on, the original performance can often reached with COTS
systems.

If some old military system used a card full of TTL chips to implement
a multiplier, the same could be implemented with a COTS micro
controller (assuming temperature and radiation requirements would not
be a problem) with plenty of I/O pins. The _only_ thing the micro
controller would do to read the multiplier and multiplicand from input
pins, perform the multiplication and write the product to the output
pins. Of course, the modernisation and testing of this module would
have to be done at a scheduled time (e.g. every 5 or 10 years), thus
hopefully before any large scale production is needed.

No PC104, it can't handle the environment (-55 deg C high vibration)
or the size and power constraints, or the crazy power thats available
on an aircraft (alternators) Custom operating systems and custom
hardware are standard issue.

See page 13. According the the catalog it uses an Intel 166 MHz processor
with Windows NT or CE.

Here is a quote from their catalog:

"The Navigator 10.4cTS is a compact, embedded Intel® PentiumT based
hardened PC designed for use in rugged outdoor environments. The
system incorporates a 10.4? transflective LCD for superior viewing in
high light conditions with a broad-range dimmable back-light for viewing
in low light conditions. The integrated high-light rejection infrared
touch-screen provides a means for reliable operator input in extreme
operating conditions."